Treatment machine and method of improving a cutting edge

ABSTRACT

A treatment machine for adjusting a K factor of a cutting edge of a worktool is described. In an embodiment the treatment machine comprises: a blast gun for directing a pressurised blast stream of abrasive particles in a blast direction; mounting means for securing the worktool such that a rotational axis of the worktool is radially offset from the blast direction by an offset distance, and wherein control of the offset distance between the blast direction and the rotational axis adjusts the K factor of the cutting edge.

FIELD OF INVENTION

The current invention relates to a treatment machine. In particular, it relates to a treatment machine and a method of adjusting the K factor of a cutting edge.

BACKGROUND OF THE INVENTION

The reliability and performance of cutting tools, such as drill bits, end mills, slot mills, thread taps and the like, has become a more understood and controllable aspect in recent years. The microgeometry of cutting edges influences tool life, stability of the cutting process, chip formation, surface quality as well as head and force loads on the tool. It is known that creating a radius on the cutting edge (often referred to as honing the edge) can improve the life of the edge. It has also been shown that the shape of the hone cross section is important.

One approach, used in WO9735686 describes the advantages of wet blasting over brushing to hone cutting edges of elongate rotary tools. This uses a circular cross section abrasive stream to create a relatively uniformly honed cutting edge. However this document fails to describe how to create an adjustable, yet repeatable non-uniform hone.

This hone cross section shape can be from a constant radius to an increasing or decreasing radius. The symmetry of this is currently known as the K factor. K is defined as:

$K = \frac{S\gamma}{S\alpha}$

where Sy is the distance from the apex of the chipping (or rake) surface and clearance (or flank) surface to the end of rounding on the chipping surface and Sa is the distance from the apex to end of rounding on the clearance surface. Accordingly, a symmetrical cutting edge microgeometry has a K factor of 1, whilst a larger factor of K>1 indicates more rounding on the rake face or chipping surface, whilst a K factor of K<1 indicates more rounding on the flank face or clearance surface.

Different sized and radius shapes can be achieved by blasting, brushing, magnet or drag finishing, or by laser. Focussing on blasting, one method of creating an edge radius is by wet blasting. In wet blasting abrasive blast material is combined with a liquid to create a blast slurry, which is then passed through a nozzle of a blast gun or the like at high pressures. The impact of the pressurised slurry or treatment material cleans and ablates the surface to create the desired finish.

The amount of material removed is controlled by several variables: the blast pressure of the gas, the angle of the blast stream to the cutting edge, and the size, shape and density of the abrasive particles being used.

The K factor is more difficult to control and has up to now been attempted by adjusting the angle of the blast stream in relation to the rotational axis of the tool.

The present invention aims to at least ameliorate the aforementioned disadvantages by providing a more controllable method of adjusting the K factor on cutting edges.

SUMMARY

According to a first aspect of the present invention, there is provided a treatment machine for adjusting a K factor of a cutting edge of a worktool, said treatment machine comprising: a blast gun for directing a pressurised blast stream slurry of abrasive particles in a blast direction; mounting means for securing the worktool such that a rotational axis of the worktool is radially offset from the blast direction by an offset distance, and wherein control of the offset distance between the blast direction and the rotational axis adjusts the K factor of the cutting edge.

The present invention provides a more controllable machine for adjusting K factor of cutting edges. As opposed to conventional techniques, which focus on adjusting a blast pitch angle relative to the rotational axis of the worktool, the present invention focusses on the offset distance between the blast stream and the rotational axis worktool.

It can be appreciated that the blast direction may comprise a blast axis, which may or may not be perpendicular to the longitudinal axis of the worktool. In embodiments, the blast gun is positioned a blast distance from the worktool at a blast angle. The blast direction or blast axis is then the direction in which the blast stream slurry is incident against the worktool. It may be considered that the centre of the blast stream incident on the worktool is an origin and the blast gun is positioned a blast distance r at blast angle θ, where r and θ are polar coordinates describing the position of the blast gun relative to the worktool.

As an example, a radial offset distance that aligns the blast direction of the blast stream to be symmetric about the cutting edge provides a K factor of approximately 1. If the offset of the blast stream is offset towards the chipping surface then the K factor can be controlled to be >1. Alternatively, if the offset is away from the chipping surface a K factor can be controlled to be <1.

In some embodiments a blast pattern (being a broad cross-sectional shape of the blast stream) of the blast stream may be non-circular. In an embodiment rectangular blast patterns may be used. This arrangement can aid control of the offset distance between the blast stream compared to when using a circular blast pattern due to the non-linear blast profile presented by such a blast pattern to the worktool.

According to an embodiment, the blast pattern may be substantially rectangular such that the long edge of the pattern is directed at the cutting edge. The blast pattern may have an aspect ratio of at least 2:1, or may be 5:2, 3:1, 4:1 or greater.

In some embodiments the blast pattern comprises a sharp edge. Such sharp edge may be incident against the cutting edge.

In embodiments the blast gun of the treatment machine comprises a nozzle for ejecting the pressurised blast stream of abrasive particles in the blast direction. In a further embodiment the nozzle comprises a slot having a sharp edge, said sharp edge providing a corresponding sharp edge in the blast pattern. In other words, the long edge of the pattern is the sharp edge.

Generally the worktool may be a drill bit, end mill, thread tap or slot mill. When the worktool is a drill bit, the cutting edge may be the edges of the flute of the drill bit. The cutting edge may also refer to the edges of the point angle. (end cutting edges).

The worktool often comprises a round shank, however it can be appreciated that hexagonal, square, trigonal, triangle or other cross-sectional shanks may be used.

In embodiments, the abrasive particles comprise one or more of particle types such as glass beads, metal shot or aluminium oxide particles. Mixtures or combinations of abrasive particles may be used, with such mixture being tailored to the required finish and materials used. These blends of different abrasive materials can have opposing or complimentary properties—one example blend is glass beads and virgin white aluminium oxide. Virgin aluminium oxide is often used in applications where the worktool may be liable to rusting due to the low iron content of this type of aluminium oxide.

In preferred embodiments, the pressurised slurry is a wet blast slurry comprising a mixture of the abrasive particles and compressed gas with a liquid to form a pressurised slurry, lubricating the abrasive particles in a buffer of liquid (typically water, although additives may be used to prevent rusting, prevent organic build-up, or the like).

In a second aspect of the present invention there is provided a method of improving a cutting edge of a work tool, said worktool having a rotational axis, wherein the method comprising the steps of: securing the worktool within a blasting chamber, said blasting chamber comprising a wet blast gun for ejecting a stream of abrasive particles suspended in a slurry, out of a nozzle of the blast gun; directing the stream of abrasive particles at a cutting edge of the work tool; and adjusting a radial distance between the nozzle of the blast stream and the rotational axis; wherein the blast nozzle is configured to produce a substantially non-circular cross-section blast stream and wherein the nozzle is aligned substantially perpendicular to the rotational axis.

It can be appreciated that the embodiments and examples described in relation to the first aspect can be applied to the second aspect.

Example of K factor control using the present invention will allow the K factor to be adjusted to within an accuracy of 0.02, with a range of K factor values of between 0.4 and 1.9 achievable, with typical control at the accuracy quoted at K factor values of between 0.5 and 1.8. This can be achieved whilst creating a radius of <50 microns.

These and other aspects of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiment of the invention shall now be described in detail by way of example and with reference to the accompanying drawings in which:

FIG. 1 shows an illustration of how to determine a K factor of a cutting edge;

FIG. 2 shows a treatment machine comprising a blast gun according to the present invention, and focussed towards a worktool;

FIG. 3 shows the treatment machine of FIG. 2 arranged in a configuration according to the present invention, where the worktool is aligned perpendicular to a blast stream of the blast gun and with a radial offset;

FIG. 4 shows a semi-stylised view of how a blast pattern of the blast stream is directed towards the worktool;

FIG. 5 a shows a nozzle for the blast gun of FIG. 2 according to an embodiment of the present invention;

FIG. 5 b shows an exploded view of FIG. 5 a ; and

FIG. 5 c shows a cross-sectional view of FIG. 5 a.

It should be noted that the Figures are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of the Figures have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar feature in modified and different embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows how a K factor of a cutting edge for a worktool (or indeed for any cutting edge) is determined. As shown, the cutting edge 10 comprises a chipping surface 12 or rake face and a clearance surface 14 or flank face. As can be seen from the figure, an edge 16 has an edge radius that is an approximation of the radius of a circle 20. To determine the K factor of this edge (using the technique described above) where Sy is the distance from the intersection of the chipping (or rake) surface and clearance (or flank) surface to the end of rounding on the chipping surface, distance 22, and Sa is the distance from the aforesaid intersection to the end of rounding on the clearance surface , distance 24.

FIG. 2 shows a blasting machine 40 according to a present embodiment of the current invention. The blasting machine broadly comprises a blast gun 50 having a first inlet 52 through which a slurry of abrasive particles, such as glass beads, sand, metal shot, aluminium oxides or any suitable blasting media, including mixtures of such abrasive particles, mixed with a fluid, typically water to form a slurry, is combined with compressed gas from a second inlet 54. This forms a pressurised blast stream that is directed at a worktool 60. The worktool has a rotational axis 62 and is shown as a drill bit, having spiral flutes (which can also be side cutting edges) 64 and end cutting edges 66.

In a configuration, the blast axis, or blast direction 72 of the blast gun 50 is aligned a blast distance 74 from the worktool at a blast angle 76. The intent is to utilise the blast pattern of the blast stream to peen and/or hone the side cutting edges 64 and the end cutting edges 66. Prior efforts have focussed on adjusting the blast distance 74 and the blast angle 76 to create the desired K factor for the cutting edges.

FIG. 3 shows the blasting machine 40 arranged in a configuration according to embodiments of the present invention. In these embodiments, the blast axis 72 is arranged perpendicular to the rotational axis 62 of the worktool 60. However, in addition to this difference from the prior art configuration, the blast axis 72 is offset from the rotational axis 62 by a radial offset distance 80. In embodiments, a radial offset of 0 provides a K factor of approximately 1. If the offset of the blast stream is offset towards the chipping surface then the K factor can be controlled to be >1. Alternatively, if the offset is away from the chipping surface a K factor can be controlled to be <1. As an example, a range of K factor values of between 0.4 and 1.9 is possible, with an accuracy of 0.02. This corresponds to an accuracy of the edge radius of <50 microns. Accordingly, by adjusting the offset distance the K factor of the cutting edge to be selected with a high degree of accuracy. It can be appreciated that the blasting machine may still be arranged at a blast angle 76, however in this embodiment the offset distance 80 is varied to adjust the K factor accordingly.

FIG. 4 shows the worktool 60 when subjected to a directed blast stream from the blasting machine of FIG. 3 . In particular, the effect of blast stream pattern or shape can be seen. With a circular blast pattern 80 the blast media is difficult to align at the cutting edges of the flutes 64 or the end cutting edge 66—this leads to either wasted blast media, or more likely to an inaccurate finish, making control of the K factor of cutting edges difficult. It can be appreciated that an attempt to adjust the K factor of middle flutes 64 is likely to also affect already treated lower flutes leading to inconsistent results.

Conversely, embodiments of the present invention utilise a non-circular blast pattern 90, such as a rectangular blast pattern. The use of such a blast pattern, particularly with the above described configuration allows for a greater control and adjustment of the K factor of the cutting edges. Typical non-circular blast patterns are rectangular, although square or elliptical patterns may also be used depending on the shape of the cutting edge to be honed. Typical aspect ratios for such non-circular blast patterns are 2:1, although 5:3, 3:1, 4:1 may also be used. The use of a thin blast pattern with this blasting machine configuration allows the K factor to be adjusted in a finer manner than previously.

An exemplary embodiment of a nozzle 100 for producing a non-circular blast pattern 90 is shown in FIGS. 5 a to 5 c . Such nozzle 100 has a substantially rectangular or square shaped slot or end nozzle 110 from which the slurry of abrasive particles may be ejected. Said nozzle 100 comprises a base portion 120 having a sloped base surface 122. It can be appreciated that the end nozzle 110 has a sharp edge. The sloped base portion extends into a flat base portion 124. Said flat base portion 124 extends into the nozzle 100. An air guide 130 is connected above the base of the nozzle past the flat base portion 124. The air guide 130 is a broadly flat surface having a chamfered end surface 131 that meets the end of the slot 110 as the slot opens out into a larger slurry chamber . The air guide 130 is secured by screws 140. The air guide 130 is secured above the base of the nozzle base surface 124 to allow a channel 139 through which air can pass via an air inlet 138. In addition to the air guide 130, a slurry guide 132 is provided. The slurry guide 132 is co-located opposite the air guide but is located opposite the sloped base surface 122 and the flat base portion 124 within the slot 110. A chamfered edge 133 is also provided. The slurry guide is secured to a top plate 134 of the nozzle using screws 142.

The top plate caps the nozzle, leaving an exposed rectangular opening at the slot 110. The top plate comprises a slurry entry point or hole 136 through which slurry may be injected. The top plate secures the air guide 130, slurry guide 132 and the top plate 130 to the base portion 120 using screws 148, washers 146 and nuts 144.

In use, as shown in FIG. 5 c , air is injected into the nozzle at inlet 138. The air passes along channel 139 before exiting opposite the air guide 132. Similarly, a slurry of abrasive particles enter via slurry inlet 136. The slurry is guided by the slurry guide 130, down chamfer 131 and against chamfer 133 of the air guide. At this point it mixes with the pressurised air from the air inlet 136. The pressurised air/slurry mixture is then guided via the air guide towards the nozzle end slot 120 where the pressurised blast stream exits. The sloped base portion 122 of the base portion 120 and the shape of the slot create a substantially rectangular shaped blast stream. It can be appreciated that rectangular (or square, or other non-circular) shaped blast stream formed by the correspondingly shaped end nozzle slot 112 provide a sharp edge to the blast stream, rather than a traditional funnel shaped blast stream from a conventional circular nozzle.

From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of wet blasting, and which may be used instead of, or in addition to, features already described herein.

Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub combination. The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

For the sake of completeness it is also stated that the term “comprising” does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality, and reference signs in the claims shall not be construed as limiting the scope of the claims. 

1. A treatment machine for adjusting a K factor of a cutting edge of a worktool, said treatment machine comprising: a blast gun for directing a pressurised blast stream of abrasive particles in a blast direction; mounting means for securing the worktool such that a rotational axis of the worktool is radially offset from the blast direction by an offset distance, and wherein control of the offset distance between the blast direction and the rotational axis adjusts the K factor of the cutting edge.
 2. The treatment machine of claim 1, wherein a blast pattern of the blast stream is substantially non-circular having an edge, such that the edge of the pattern is directed at the cutting edge.
 3. The treatment machine of claim 2, wherein the blast pattern is substantially rectangular.
 4. The treatment machine of claim 3, wherein the blast pattern has an aspect ratio of at least 2:1.
 5. The treatment machine of claim 2, wherein the blast gun comprises a nozzle from which the blast stream is ejected, and wherein an outlet of the nozzle is substantially non-circular.
 6. The treatment machine of claim 1, wherein the worktool is a drill bit, end mill, thread tap or slot mill.
 7. The treatment machine of claim 1, wherein the worktool comprises a round shank.
 8. The treatment machine of claim 1, wherein the abrasive particles comprise one or more of glass beads, metal shot or aluminium oxide particles.
 9. The treatment machine of claim 1, wherein the offset distance is the offset relative to a chipping surface of the worktool.
 10. The treatment machine of claim 9, wherein an offset symmetric about the cutting edge provides a K factor of approximately
 1. 11. The treatment machine of claim 9, wherein an offset towards the chipping surface provides a K factor of greater than 1, and an offset away from the chipping surface provides a K factor of less than
 1. 12. The treatment machine of claim 1, wherein the range of K factor values is between 0.4 and 1.9.
 13. A method of improving a cutting edge of a work tool, said worktool having a rotational axis, wherein the method comprising the steps of: securing the worktool within a blasting chamber, said blasting chamber comprising a wet blast gun for ejecting a stream of abrasive particles suspended in a slurry, out of a nozzle of the blast gun; directing the stream of abrasive particles at a cutting edge of the work tool; and adjusting a radial distance between the nozzle of the blast stream and the rotational axis; wherein the blast nozzle is configured to produce a substantially non-circular cross-section blast stream and wherein the nozzle is aligned substantially perpendicular to the rotational axis. 